1. Field of the Invention
The present invention relates to a color image forming apparatus and a color image forming method to obtain a color image by superposing a number of plural color images formed using plural image carriers with an electro-photographic copying machine, a printer, etc.
2. Description of the Related Art
For a color image forming apparatus such as copying machine, printer, etc., it is demanded to speed up image forming time, get color image of good color reproduction, prevent deterioration of various consumables for color image forming when forming monochromatic images, and decrease scattering toners generated when transferring images. In the Japanese Patent Application Publication No. 2003-186281 or 2004-205944, an image forming apparatus capable of forming color images on recording paper using color image forming units provided with plural color photosensitive drums arranged in tandem and forming monochromatic images on recording paper without driving color image forming units by a black image forming unit provided separately from color image forming units to form a black toner image on a black photosensitive drum are disclosed. In either of these conventional image forming apparatus, the black image forming unit only is used for forming monochromatic images with sharp image quality without using various consumables for the color image forming unnecessarily to prevent deterioration of consumables and decrease scattering of toners. Further, when forming color images, color images of good color reproducibility are obtained according to the intermediate transfer system.
On the other hand, for a color image forming apparatus which consumes much toner, use of recycled toners for saving toners is demanded in recent years. In the Japanese Patent Application Publication No. 248047, an image forming apparatus which recovers toner remaining on photosensitive drums after completing the transfer in the next image forming and developing process in the developing units at the same time of the development is disclosed. When such developing units for cleaning remaining toner at the same time of the development are used, it is not necessary to arrange cleaners around photosensitive drums and an apparatus in smaller size can be achieved, abrasion of photosensitive drums by cleaners is prevented extending the life of the apparatus and at the same time, consumption of toner can be saved by recycling recovered toner.
However, even when developing units which clean residual toner at the same time of the development were used, toner adhered on, for example, the transfer belt which conveys recording paper were recovered by a cleaner of the transfer belt in the past. On the other hand, when the intermediate transfer system is used to transfer color toner images on the intermediate transfer medium on a recording paper in lump after superposing them on the intermediate transfer belt in order to improve the color reproducibility in the color image forming, toner adhered on the intermediate transfer belt are recovered by an intermediate transfer belt cleaner. Furthermore, each cleaner must perform the recycle process or disposing process of the recovered toner, and the toner recovery becomes complicated and impedes the effective toner recycling use.
Therefore, in a color image forming apparatus suited to both the color image forming and the monochromatic image forming, a color image forming apparatus and a color image forming method capable of easily recovering and accelerating the recycle use of adhered toner generated from color image forming units or a black image forming unit, and further improving the efficiency of toner consumption and a color image forming method are desired.